Packers are used as barriers in boreholes to direct pressure into a formation for a treatment. Some designs are made to be retrieved. Provisions are made at opposed ends of sealing elements to prevent extrusion. The extrusion barriers that have been tried have lacked several features addressed by the present design. One design criteria is that the ends of the sealing element need protection from swabbing when fast moving fluids are pumped past a sealing element before a packer is set. This can happen when there is a need to replace one well fluid with another before the packer is set and the pumping rates create high velocities. These high flow rates can distort the extrusion ring assembly to a point where after the set the extrusion barrier fails to accomplish its intended function.
Some designs use overlapping extrusion rings. In this design the ends of the extrusion rings radially overlap the sealing element ends for running in. The problem here can be that during the setting of the sealing element some of the rubber climbs over the end of the extrusion ring assembly such that the sealing element radially overlays the extrusion ring assembly. When this happens there is no effective extrusion barrier as the extrusion ring assembly is prevented from engaging the surrounding tubular. The end of the extrusion ring assembly could also penetrate into the sealing element and prevent the sealing element from sealing. This could also make removal of the packer more difficult as the extrusion ring assembly that is embedded into the sealing element prevents adequate retraction of the sealing element for retraction. Other potential issues of known designs include extrusion along the mandrel.
Some specific known designs will be discussed below to illustrate the shortcomings of the past designs. In FIG. 1 a sealing element 10 is flanked on opposed ends with a Teflon® spacer 12 and then a wire mesh ring 14. The unset position is shown. The issue with this design is that if there is a high velocity circulation rate past the unset sealing element 10 the wire mesh is too soft to resist those high velocities and can be pushed into the extrusion gap causing damage to the wire mesh preventing it from performing properly. The design intent is to make the wire mesh ring 14 soft enough to move with the sealing element 10 out to the surrounding tubular that is not shown. If the wire mesh is made stiff then the sealing element 10 can climb over the mesh ring 14 during the set in which case the ring 14 will not prevent extrusion. The ring 14 and the spacer 12 are simply abutting and can move relatively to one another during the set.
FIGS. 2 and 3 illustrate another known design where the extrusion rings 18 and 20 flank a sealing element 22. Ideally, during setting, the rings 18 and 20 move ahead of the sealing element. However, the sealing element 22 can move out faster than the rings 18 and 20 in which case the sealing element 22 can wrap around the rings 18 and 20 to defeat the purpose of the rings 18 and 20 so that there is effectively no extrusion barrier. In such cases the free ends of the rings 18 an 20 can embed into the sealing element 22 making removal extremely complicated as the rings 18 and 20 hold the sealing element out against the surrounding tubular rather than allowing the sealing element to retract away from the surrounding tubular so that the packer can be pulled out rather than getting stuck and having to be milled out.
The present invention protects the sealing element from the end of an extrusion ring with an intermediate softer layer attached to the extrusion ring such that during the set the intermediate layer sticks out axially further to protect the sealing element from the free end of the extrusion ring. The extrusion ring and the intermediate layer are affixed to each other which keeps the parts concentric to each other and restricts relative motion between the parts. The intermediate layer acts as an extrusion barrier against the mandrel. The end of the intermediate layer can fill a void space between an end of the extrusion ring and the sealing element. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.